Precision stop for hobbing machines



June 20, 1961 J. E. VAN ACKER 2,983,954

PRECISION STOP FOR HOBBING MACHINES Filed Oct. 14; 1957 4 Sheets-Sheet 1 IN V EN TOR.

JOSEPH E. VAN AOKER BY ATTORNEY June 20, 1961 J. E. VAN ACKER PRECISION STOP FOR HOBBING MACHINES 4 Sheets-Sheet 2 Filed 00 14, 1957 INVENTOR.

JOSEPH E. VAN ACKER waiimw ATTORNEY June 20, 1961 J. E. VAN ACKER PRECISION STOP FOR HOBBING MACHINES 4 Sheets-Sheet 3 Filed Oct. 14, 1957 unm uuunnllml 4 m o w w I :L 1 F x m P 0 a mm :m J

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JOSEPH E.VAN ACKER ATTORNEY llnitcd States Patent Ofiice z PRECISION STOP F The present invention relates to machine tools and more particularly to an improved method and means for controlling automatically the cycle of movements of the hob of a bobbing machine. In its broadest aspects the invention is applicable to hobbing machines adapted to cut teeth on spur, helical, and worm-gears utilizing radial, axial, or tagential movements or a combination of two or more of such movements of the hob relative to the work blank and/or in combination with different rates of feed in the same or different directions.

A primary aim of the invention is to provide a practical means for bringing a power-shifted element of a machine, such as the cutter stanchio'n of a hobber, to a positive stop at a precise point, such as cutter depth, and immediately thereafter initiate into action one or more trains of mechanisms that cause the hob to move in a different direction at the same or a different rate of feed until the bobbing operation has been completed, and thereafter to return the hob and the cutter stanchion automatically to their original starting positions.

Another important aim of the invention is to provide a system of electrically operated, mechanized controls for the various feed, speed, and direction clutches customarily used in hobbing-machine transmissions, so constituted and arranged that any given program or automatic cycle of hob movements relative to the work blank may be instantly obtained without undue supervision by the operator or the manual shifting of the various clutches.

In the embodiment about to be explained a vertical hobber is taken as a typical example and in which the work blank revolves on a vertical axis, the cutter stanchion is movable radially at traverse and one or more cutting rates, and the hob and hob slide are movable vertically at traverse and one or more feed rates. By means of a special attachment (not disclosed) the hob spindle may be given a tangential movement useful in the hobbing of wormgears. Considering, however, only the hobbing of spur gears in which no special attachment is required such gears may be hobbed (l) by traversing the hob radially of the work to the proper depth and then feeding the hob up (or down) first at a relatively fast feed rate until the hob is about to reach its full cut and then at a relatively slow feed rate until the cut is finished, then traversing the stanchion out and the hob down (or up) to starting position; (2) by feeding the hob into depth, then up (or down) at the same or a different rate, then traversing out and down (or up) to the point of starting.

Each of the examples given above embrace, it will be seen, at least four different operational cycles depending upon the method of hobbing preferred and each of which, with this invention, is made selectively available. A preferred method of rendering the operational cycles selectively available includes the provision of an improved means for bringing the cutter stanchion to a positive stop at a precise point, the provision of solenoid-controlled fluid-actuated clutches, solenoid-operated magnetic starters for the motors, and the provision of multipole tap switches, control relays, manual-selector switches, and cycle-selecting means which function to coordinate the various circuits and to provide the hobber with a selective automatic sequencing system.

In accordance with this invention, all of the taps of the multipole switch (stepping switch) and all of the con- 2,988,9(54 Patented June 20, 1961 nections to the coils of the function-control relays are brought to separate terminations in a multicontact socket. The bridging of selected pairs of these terminations completes portions of the circuits of the control relays which will become activated in sequence as the stepping switch is pulsed. Control relays Whose circuit terminations at the socket remain open or unbridged to stepping-switch taps do not of course function. By employing a complementary plug having prongs mating the terminations in the socket and having certain prongs interconnected, the insertion of such plug in the socket automatically completes portions of a number of circuits whose control relays are brought into action in the sequence determined by the pulses given to the stepping switch. By interconnecting certain prongs of individual plugs a plurality of operational programs or machine-cycle functions can be prearranged and merely by inserting the proper plug for a given machine cycle the machine may be caused automatically to perform that particular operational cycle.

Other objects and advantages will be in part indicated in the following description and in part rendered apparent therefrom in connection with the annexed drawings.

To enable others skilled in the art so fully to apprehend the underlying features hereof that they may embody the same in the various ways contemplated by this invention, drawings depicting a preferred typical construction have been annexed as parts of this disclosure and, in such drawings, like characters of reference denote corresponding parts throughout all the views of which:

FIG. 1 of the drawings is a view of a gear-bobbing machine embodying this invention.

FIG. 2 is an enlarged view of a portion of the machine shown in FIG. 1 and illustrating more clearly portions of the feed screw, feed shaft, gearing, clutches, and their actuators.

FIG. 3 is a plan view of a portion of FIG. 2 illustrating more clearly the stanchion infeed-position stop and its out-travel co'ntrol.

FIG. 4 is an enlarged detail view of the stanchion feedscrew mounting assembly at the gear-box end thereof.

FIG. 5 is a diagrammatic developed view of the entire bobbing-machine transmission.

FIG. 6 is a diagrammatic view of the fluid system and solenoid valves for sequentially operating the various clutches.

FIG. 7 is a diagram of the control circuits for the motors and functional relays.

FIG. 8 is a diagram of cycle-selector bridging-plug connections for an lnfeed-Upfeed cycle.

FIG. 9 digrammatically illustrates the path of movement of the hob produced when using the cycle-selector plug of FIG. 8.

FIG. 10 is a diagram of cycle-selector bridging-plug connections for a rectangular Upfeed cycle.

FIG. 11 diagrammatically illustrates the path of movement of the hob produced when using the cycle-selector plug of FIG. 10.

Referring more particularly to FIG. 1 of the drawings, the hobbing machine illustrated comprises a main base member 50 having horizontal guideways 51 along its top on which a cutter stanchion 52 is slidably mounted. The forward portion of the base provides bearings for a rotatable work spindle 53, the upper portion of which mounts a work table 54 on which one or more work pieces 55 are clamped. The work spindle is driven by worm and wormgear mechanisms 56 and from powertransmission mechanisms housed primarily in a gear box 57 located at the right-hand end of the machine.

The stanchion member 52 is provided with vertical guides 58 on which is mounted a vertically movable cutter slide 59. The forward face of the cutter slide mounts a hob swivel head 61) that provides bearings for a rotatable hob spindle 61 which carries a hob 62 in operative relation to the workpieces 55. The hob spindle also receives its power from the transmission elements in the gearbox and both hob and work spindles are driven in timed relation as is customary in the hobbing of gears. According to the nature of the hobbing process, the stanchion may be power shifted toward and away from the work-spindle axis and the cutter slide power shifted up and down. In the instant embodiment both shiftable members are moved by screw and nut means driven from the transmission elements contained within the gear box 57.

Speed train The complete drive is illustrated in developed form in FIG. 5. In the machine shown, power from a main motor M1 enters the machine through belt-drive element 65 and thence through pick-01f speed-change gears 66 and reversing clutch 67, drives shaft 68. Shaft 68 transmits power through gears 69 to horizontal. splined shaft 70 and the latter, through bevel gears 71, transmits to a vertical shaft 72 located adjacent the front of the stanchion. A similar pair of bevel gears 73 transmits power to a horizontal shaft 74 journaled in the cutter slide. Shaft 74 drives a wormgear assembly 75 at the pivotal axis of the swivel head 60, and bevel gears 76, shaft 77, and spur gear 80 drive the hob spindle 61 and the hob 62.

The work-spindle drive is taken off the cutter drive by gears 81 and differential shaft 82. If the casing of the differential unit 83 is locked, power flows through to shaft 84 to index change gears 85 and thence through a horizontal shaft 86 to the work-table wormgear drive assembly 56. Through the transmission described, the work spindle and hob spindle are driven in timed relation at the speeds determined by the ratios of the gears used in the indexand speed-change-gear assemblies 85 and 66, respectively.

Feed train (vertical) Power to move the stanchion in and out and the cutter slide up and down at one of two selectively available cutting rates is taken off the work drive shaft 86 by bevel gears 87' and worm shaft 88 to ratio change gears 89 to another worm shaft 90; Wormgear units 91 and 92 connected with the respective worm shafts and a shiftable feed-ratio clutch spool 93 transmit the power at one of two rates to shaft 94 and feed-change gearing 95. The

terminal drive gear of this train normally runs loose in a bearing 96 and is provided with clutch teeth at its inner side. An Off-On feed-clutch spool 97 splined to a stub shaft 98 is provided to connect and disconnect the power feed. Shaft 98 extends forward and when coupled with a coaxial shaft 980, drives through gears 99, wormgear unit 100, and gears 101 to a vertically arranged feedscrew shaft 192. The vertical feed screw 102 threadably engages a feed nut carried by the cutter slide and by means of which the slide and hob carried thereby may be power shifted at either one of the two feed rates up or down.

Feed train (radial) outer end of the stanchion feed screw 108. The feed screw extends forward and threads a nut 109 that is secured to the underside of the stanchion 52.

Lead gearing When the clutch gear unit 103 is shifted to its other extreme position it engages with gear 110, on the feed shaft 98a, which meshes with a gear 111 on a shaft 112. Bevel gears 113 (not labeled in FIG. 5) transmit the power to a shaft 114 and lead change gears 115. The terminal lead gear drives a shaft 116 that conveys the power to a wormgear unit 117 operatively associated with the casing of the differential unit 83 and thus imparts an additive or subtractive movement to the work-spindle drive during the hobbing of helical gears, casing 83 bc ing unlocked.

Rapid traverse When the Off-On clutch 97 is in Off position the power feed is disconnected so that the stanchion 52 or the cutter slide 59 may be moved at a traverse rate. For this purpose a traverse motor M2 of the reversible type is embodied in the organization which, when in motion, transmits power through a belt drive 118 to a shaft 119 and thence through a chain and sprocket drive 120 to the stub feed shaft 98. If the direction clutch unit 193 is in its extreme right position (as viewed in FIG. 2) the stanchion feed screw 108 is operated at a relatively fast rate, whereas if the direction clutch 103 is in its extreme left position the stanchion horizontal feed screw is disconnected and the feed shaft 98a and hob-slide vertical feed screw 16?; are operated at a relatively fast rate. Should the machine be set up for bobbing helical gears the lead gearing 115 will also be effective when the clutch 163 is in the position last mentioned.

From the foregoing it will be seen that an exceptionally versatile hobbing machine has now been provided incorporating not only the usual hoband work-spindle drives but power-feed means electively operative in a radial direction, and in an axial direction at either of two cutting feed rates in the respective directions. That is, for example, one feed rate may be employed to feed the hob in a radial direction and the other feed rate employed to feed the hob in an axial direction in combination with rapid traverse of the hob back to the starting point, or two different feed rates may be used in one direction in combination with rapid traverse back to the starting point. It is a primary aim of the invention to program the desired methods of hobbing and to cause the machine to carry out the selected program or function cycle automatically.

To that end the feed-ratio clutch 93 (fast feed/slow feed) the rate clutch 97 (feed-Oif-On), and the direction clutch 103 (radial-vertical) are power operated, solenoidvalve controlled. An electrical control system is provided, as will later be explained, to effect actuation of the respective clutches in a prearranged sequence. At this point it may be explained that the stopping of the hobcarrying stanchion at a precise point for the size of the gear to be hobbed is most critical, and this in combina tion with the feature of automatically changing the direction of hob feed after that precise point is reached, poses a difficult vproblem not heretofore encountered or solved in a practical and economical manner. Among the features contributing to the solution of this problem of distance and sequential movements of different but cooperating elements is the conception of mounting the stanchion feed screw 108 in a manner as to yield axially slightly when the stanchion is brought thereby up against a fixed stop and to utilize the slight yield to initiate a sub sequent function. The improved feed'screw mounting is illustrated most clearly in FIGS. 2, 3 and 4, and consists in telescoping the feed-screw shaft 198 in a rotatable but nonshiftable drive sleeve 167. The sleeve is journaled in recessed antifriction radial-thrust bearings and 151 in the gear box 57 and is formed with a shoulder 107a at one end that abuts bearing 151 and a threaded forward end that receives a clamp nut 152 that abuts bearing 150. With this construction the sleeve is freely rotatable but clamped against shifting movement in the gear box. The gear 106 previously mentioned is keyed and locked to the sleeve as at 106a and the horizontal feed screw 108 is turned down as at 10812, the turneddown position being splined to the sleeve as at 10811. The turned-down portion of the feed-screw shaft also extends forward a short distance beyond the sleeve 107 and carries a shouldered collar 153 that butts against the end of sleeve 107. Over the collar are placed opposed pairs of heavy disc-like springs 154 that are clamped between the shoulder on the collar 153 and a nut 155 fitted to the threads on the feed screw 108. Where the reduced portion 108a of the feed screw joins the larger and threaded portion a shoulder 1080 is formed, which, when the parts are assembled and the springs preloaded to resist any expected end thrust incident to moving the stanchion and feeding the hob into the work blank, will lie a short distance away from the end of the shouldered collar 153 and form a gap 156 between. This gap is preferably covered by a ring 157. Thus under all normal loads the feed-screw shaft is rotatable but nonshiftable and it is only when the stanchion is positively stopped as by a fixed abutment, that continued turning of the screw, by power applied to the sleeve-mounted gear 106, will the screw back out of the stanchion nut 109 and move axially rearwardly. This axial movement is herein utilized to actuate a limit switch lLS that forms part of a control circuit that initiates subsequent functions. As illustrated in FIG. 4, the screw shaft extends through the sleeve and carries a nut 158 that overlays the shouldered end of the sleeve and prevents withdrawal of the screw shaft therefrom. The screw shaft also carries a threaded stern 159 at its outer end which may be adjusted in or out to obtain the correct location for actuating the adjacently mounted limit switch ILS when the screw shaft has backed out against the pressure of the heavy springs 153 the permissible distance relative to the sleeve.

The fixed abutment against which the stanchion 52 moves is illustrated more clearly in FIGS. 2 and 3 and includes a screw shaft 160 secured to and movable with the stanchion, a fixed lug 161 secured to the gear box 57 and through which the screw 160 passes, and an adjustable nut 162 that threadably engages the screw shaft 160. The nut 162 is formed preferably in two parts, the one acting as a jam nut for the other, with one part circumferentially scribed, or formed with an angularly adjustable calibrated sleeve, to cooperate with a fixed scale 163 carried by the stationary lug 161. Thus, according to the setting of the nut 162 on the screw 160 the stanchion will be moved forward (in) until the nut engages the abutment 161 and stops further movement of the stanchion at that precise point. Thereafter the feed screw 108, which continues turning, backs out slightly, compressing further the preloaded disc springs 153 until the limit switch 1LS is actuated to institute other functions. On the reverse movement of the stanchion, a second twopart nut 164 adjustably mounted on the shaft 160 will, at the desired point in the back travel, engage and operate another limit switch ZLS to initiate other functions.

Pneumatic system The several clutches herein referred to are adapted to be actuated pneumatically, the dual-feed clutch 93 by air cylinder 193 operating through bell-crank lever 194; the Off-On rate clutch 97 by air cylinder 197 operating through lever 198; and the direction clutch 103 (horizontal-vertical) by air cylinder 203 operating through lever 204. The valves and pneumatic system that control the operation of the air cylinders are illustrated in the FIG. 6 diagram in which line 250 indicates a source of air under pressure that may be filtered by the unit 251, regulated as to pressure for operating purposes at the regulator 252, and lubricated for machine use by the unit 253. Pressure air leaving the lubricator is conducted by line 254 to each of three solenoid-operated valves 297, 303, and 293. These valves are of commercial design and construction and need not, it is believed, be explained in detail except to say that each includes a ported casing and a ported spool or valve core that is shiftable endwise therein by means of solenoids and/or springs. The direction of flow of pressure air through the valves is indicated by the arrows thereon, one line leading to one end of an associated air cylinder and the return from the other end of that cylinder leading back to the valve where it discharges to atmosphere. When the valve spools are shifted to the opposite position from that indi cated in the diagram the air pressure is directed to the opposite ends of the respective air cylinders and the air entrained ahead of the pistons thereof discharges to atmosphere. The pistons of the several air cylinders are mechanically connected to their respective clutch spools as previously described and when actuated to one position or the other in response to a shifting of the solenoid valves effect a shifting of the clutches to stop or start a movement or to condition the transmission for another function.

Briefly, the operation of the individual combinations of air valves, solenoids, air cylinders and clutches is as follows:

Feed clutch 97: Solenoid 97 is de-energized and the spring associated with valve 297 has pushed the valve spool to the right and pressure air enters the large end of cylinder 197 to effect shifting of the feed clutch to its Off position. (The Off position of the feed clutch imparts two facts(1) the power feed is disengaged and (2) the rapid traverse connected ready for operation whenever traverse motor M2 is energized for either forward or reverse direction motion.) When the valve solenoid 97 is energized the valve shifts to the opposite position wherein pressure air is directed to the rod end of the air cylinder and the feed clutch 97 is shifted to its On or powerfeed-engaged position and the rapid-traverse train is inoperative.

Dual-feed clutch 93: When valve solenoid 93 is deenergized the valve spring shifts the valve to the right directing pressure air to the rod end of cylinder 193 retracting the piston and moving clutch spool 93 to the left in engagement with wormgear 91, the faster of the two feeds available. When the valve solenoid 93' is energized the valve spool shifts to the left in opposition to its spring, and air is directed to the piston end of the cylinder to expel the piston and move clutch spool to the right in engagement with wormgear 92 which is the slower of the two feed rates.

Horizontal-vertical clutch 103: When solenoid 103" is energized and solenoid 103' is de-energized the valve 303 is in position as shown in the diagram wherein air pressure is directed to the rod end of cylinder 203 and the clutch 103 is moved to the left is engagement with gear On feed shaft 98a and the train for moving the hob slide vertically is engaged and the drive to the horizontal feed screw 108 is disengaged. When valve solenoid 103' is energized and solenoid 103" de-energized, the valve 303 is shifted to its opposite position directing pressure air to the piston end of cylinder 203 which causes a shifting of the clutch 103 out of engagement with gear 110 and into engagement with gear 104 which is part of the train connected with the horizontal feed screw 108. Thus the horizontal feed is engaged and the vertical feed disengaged. In all instances the air pressure holds the respective clutches in their respective positions.

Electrical system A representative control circuit adapted to cause a hobbing machine embodying a positive stop for the cutter stanchion to perform a number of automaticcycling functions is illustrated in FIG. 7. The control circuit is divided into two parts: One part includes the solenoids of the fluid-control valves 293, 297, and 303, that control the operation of clutches 93, 97, and 103, respectively, and the solenoids of the magnetic starters for the motors M1 and M2, normally operable 0n -v. AC. The other part includes a stepping switch 210, step 7 control relays 1CR, ZCR, 3CR, and QCR, function control relays SCH-MGR, manual control switches Run, Stop, and Reset and a cycle selector plug (or plugs) 211, two of such plugs being shown diagrammatically in FIGS. 8 and 10 for illustrative purposes.

The stepping switch 210 in the circuit illustrated is of the indirectly operated direct-current telephone type in which a circuit closure to the step magnet coil (Step) causes the magnetic field to compress a spring, and this spring then advances the stepping-switch wipers W1-W5 one step when the circuit is interrupted to release the magnet. The stepping switch has its coil circuit arranged so that an initial step can be caused only by closing a circuit through the manual control Run pushbutton, and all subsequent steps are caused by closing circuits at the completion of phases of the cycle. The stepping switch 210 also has self-interrupter contacts INT which open a circuit to the Step magnet coil as soon as the magnet pulls in its armature. This circuit which includes the self-interrupter contacts INT is used to automatically reset the stepping switch to its off position. The plurality of wipers Wi-WS and contact banks in the stepping switch are used to sequentially close circuits to selected function-control relays SCR-12CR. The stepping switch also has an off-normal contact 213 which closes upon an initial step of the switch, remains closed during all subsequent steps, and opens only When the wipers have advanced to the off or home position.

The step-control relays, 1CR, ZCR, 3CR, and 4CR are of the conventional slow-to-operate slugged-coil type and like the stepping switch are operated on direct current. The rectifier REC and capacitor CAP perform the function of rectifying and smoothing the current to operate these relays. These relays each have in addition to their regular coil a very heavy shorted single turn at the armature end of the magnet core. Currents induced in this single turn during the initial energization of the relay setup a magnetic field which opposes the regular magnetic field produced by the regular coil, and these temporarily opposed fields delay the operation of the armature. The purpose of this delay is to allow a current pulse of finite duration to pass through normally closed relay contacts before the relay operates to open the contacts. This current pulse is used to energize the stepping-switch magnet coil, and at the end of the current pulse, the magnet releases to cause the wipers to move forward one step.

The cycle-selection system comprises a socket and cycle-selector plug 211. All of the bank connections 214 of the stepping switch and all of the coils of the functioncontrol relays 5CR-12CR are each brought to separate terminations of a multicontact socket. The respective terminations are illustrated in the Y ends of connections a, b, 0, etc. of the stepping switch and the connections A, B, C, etc. of the relays 5CR-12CR. The cycle-selector plug 211 has mating prongs; selected prong terminations are interconnected to form several circuits, groups of which are sequentially employed to energize functioncontrol relays to form a machine-operating cycle. Typical cycle-selector plug connections are shown in FIGS. 8 and 10.

The cycle-selector plug connections shown in FIG. 8 cause an infeed-upfeed rectangular cycle and consists of a first step in which the hob is fed radially into the work at the slower of two selected feed rates, a second step in which the hob is fed axially (up) at the faster of two feed rates, a third step in which the main motor is halted and the hob is rapidly traversed radially out of the workpiece by means of a separate traverse motor, a fourth step in which the hob is rapidly traversed axially (down) to the point of beginning and a final step in which the stepping switch is cleared by causing it to automatically step forward to the home or off position.

The cycle-selector plug connections shown in FIG. 10 cause a simple rectangular upfeed cycle in which the first step causes the hob to be rapidly traversed radially into a preset position at which bobbing of gears to the proper depth can occur, followed by second, third, fourth, and fifth steps which are identical to those of the infeedupfeed cycle of FIG. 8.

After the operator has selected his operating cycle and inserted the appropriate cycle-selector plug 211 in the socket provided in the electrical panel at the rear of the machine, the operation of the electrical system is as follows:

lnfeed-Upfeed cycle The operator depresses the Run pushbutton which closes a circuit to both relay iCR and the stepping switch magnet coil Step. Relay contact lCRl opens to de-ener gize Step coil to cause the stepping switch wipers W1W5 to advance one step off the home position. Relay con tacts 1CR2 close and hold relay llCR continuously energized for the duration of the cutting cycle. Relay contacts 1CR3 close and supply current through the steppingswitch wipers Wit-W4 to the function relays SCR-IZCR via the cycle-selector socket and plug 211.

When the stepping switch advances to its first step off the home position, the wipers W1, 2, 3, and 4 activate terminals a, b, c, and d of the cycle-selector socket. Wiper W5 moves to transfer the Step coil from the pushbutton circuit to the circuits which include the cycle-step control relays ZCR, 3CR, and 4CR. Also the ofi-normal contact On closes on this first step to later enable relay R to be energized.

In the Infeed-Upfeed cycle, these terminals a, b, c, d, are connected via the cycle-selector plug to cause relays SCR, 7CR, SCR, and 9CR to be energized which, in turn, causes the main motor (M1) starter and the solenoids 97', 193', and 93' to be energized. Thus the respective air valves are shifted and feed clutch 97 is thrown in to engage power feed; the direction clutch 103 is moved to connect in the horizontal feed train (shaft 198) and the feed ratio clutch )3 is thrown to engage wormgear 92. This combination of functions causes the infeed screw to move the stanchion 52 in at the slower of the two available feed rates. The first portion of the stanchion movement causes limit switch ZLS to be released, causing power to be removed from ZCR relay which then releases its contacts without causing any control operation. The stanchion has fastened to it the arresting screw 169 and nut 162 which together with the abutment 161 stop the stanchion at the point predetermined by the position of the arresting nut on the screw. When the stanchion is thus arrested, the driving screw 108 being still driven by its drive gears backs up, compressing the cupped disc springs 153 beyond the amount of the preload initially set into them. When the infeed screw has backed up a small amount, the rearwardly extending anchor portion 159 of the screw pushes on limit switch 1LS to close lLSl and open 1LS2.

1LS1 closes to energize ZCR relay and the Step coil through normally closed contacts ZCRl which open and break the current through the Step coil to advance the stepping switch to the second position. At this step, horizontal and slow-feed relays 7CR and SCR are de-energized and 6CR relay (vertical) is energized in addition to the SCR and 9CR relays which are still energized. This causes the direction-selector clutch 103 to shift from the radialor horizontal-feed direction to the vertical, and causes the feed-ratio clutch 93 to shift from its connection with the slow-feed gear 92 to the connection with the normal or faster gear 91 in the feed train. The hob now commences its vertical feed. In the first portion of the vertical movement of the hob-slide, limit switch 3LS is released which de-energizes relay 30R. When the hob has finished its vertical-cutting pass through the gear blank, the hob slide 59 contacts a dog 225 on a trip rod 226 which operates limit switch 5L5. 5LS1 closes to energize 4CR relay and the step coil through relay 4CR1 normally closed contacts which open and break the current through the Step coil to advance the stepping switch to the third position, which de-energizes motor relay SCR, vertical-feed relay 6CR and feed relay 9CR, and energizes horizontal relay 7CR, and traverse-motor relay 10CR. When relay 7CR is energized, contacts 7CR1 in the circult to valve solenoid 103 close and the direction-selector clutch 1% shifts from the vertical direction to the horizontal direction. Limit switch 6L8 detects the completion of the movement of the clutch-shifting lever 204 and closes a circuit through relay contacts ltiCRl which have just been closed to cause the starter MZF of traverse motor M2 to operate, starting the motor M2 in the forward direction which, with the mechanical clutch 103 engaged for Horizontal, causes the feed screw 108 to operate and the stanchion to back out. As soon as the traverse motor starts, it drives the infeed screw 198 in the direction to relieve the pressure against the cupped-disc springs 154 and to release the operating pressure on limit switch lLS which de-energizes relay 20R. When the stanchion has backed out to the desired point, nut 164 on the arresting screw 160 pushes against limit switch 2LS to close contacts 2LS1 and open 2LS2. The opening of 2LS2 de-energizes the traverse-motor starter M2F and stops the traverse motor. 2LS1 closes to energize ZCR relay and the Step coil through relay 2CR1 normally closed contacts which open and break the current through the Step coil to advance the stepping switch to the fourth position. At this step, relay 7CR (horizontal) is deenergized and relay 6CR (vertical) is energized in addition to lilCR which remains energized. This causes the direction-selector clutch 103 to shift from the horizontal direction to the vertical direction. Limit switch 7LS detects the completion of the movement of the clutch-shift ing lever 204 and closes a circuit through relay contacts ltlCRZ which have already been closed. This causes the traverse-motor starter MZF to be re-energized, starting the traverse motor in the forward direction, which with the mechanical clutch 103 engaged for vertical causes the hob slide 59 to traverse down. As soon as the hob slide starts its downward movement, limit switch SLS is released and relay 4CR is de-energized. As the hob slide approaches the lower limit of the desired movement, it contacts a dog 227 on trip rod 228 which operates limit switch 3L8 to close 3LS1, and open 3LS2.

The opening of limit switch 3LS2 de-energizes the traverse-motor starter M2F and stops the traverse motor. 3LS1 closes to energize 3CR relay and the Step coil through relay 3CR1 normally closed contacts which open and break the current through the Step coil to advance the stepping switch to the fifth position. In the fifth position relays 60R and ltlCR are de-energized and relay 12CR is energized. Relay contacts 12CR1 hold the relay energized, contacts 12CR2 open to release relay lCR, and contacts 12CR3 close to form a circuit through the stepping switch interrupter contacts INT to Step coil. This causes the stepping-switch magnet to repeatedly energize and de-energize and causes the wipers W1, etc. to advance automatically. When the wipers reach the home position, wiper W5 has moved off the bank contacts connected to the interrupter and the Step coil cannot again be energized except by an operation of the Run pushbutton. At the same time, the oif-normal contacts On (213) open to de-energize relay 12CR which returns contacts 12CR1, 2, and 3 to their normal positions to permit a new cycle to be started.

Upfeed cycle The simple rectangular upfeed cycle is similar in operation to that just described but using, however, a plug 211 having bridging connections shown in FIG. 10. When the operator depresses the Run pushbutton in this cycle and the stepping switch moves into the first step, the first function-control relays to be energized are relays 7CR and llCR. Relay 7CR causes the direction-selector clutch 103 to shift to the Horizontal direction. Limit switch 6LS detects the completion of the movement of the clutch-shifting lever and closes the circuit through contacts 11CR2, already closed, to energize the traversemotor starter MZR. This causes the traverse motor M2 to run in the reverse direction, which with the mechanical clutch Hi3 set for horizontal, causes the stanchion to move radially in at a traverse rate. The first part of the movement causes the nut 164 to move away from limit switch 215 and relay ZCR is caused to become de-energized. At the completion of the radial movement, the arresting screw 16% and nut 162 in combination with the abutment 161 stops the stanchion. The traverse motor is still operating which causes the infeed screw to back up and compress the cupped disc springs 154 and push on limit switch 1L8. Contact 1LS2 opens to de-energize the coil MZR of the traverse-motor starter. The power is thereby removed from the motor, but the motor armature may still coast for a short time, and this coast is absorbed by further compression of the disc springs 154. 1LS1 closes to energize ZCR relay and the Step coil through relay 2CR1 normally closed contacts which open and break the current through the Step coil to advance the stepping switch to the next position. The balance of the cycle is precisely the same as steps 2 to 5 of the infeedupfeed cycle above explained.

As herein indicated the above examples of automatic cycling made possible by this invention involving a precision stop are representative of many that are available merely by inserting the proper plug 211 having the terminal connections for the desired operational sequence, and in the interests of simplifying the disclosure, a description of such additional hobbing cycles is deemed unnecessary.

Without further analysis, the foregoing will so fully reveal the gist of this invention that others can, by applying current knowledge, readily adapt it for various utilizations by retaining one or more of the features that, from the standpoint of prior art, fairly constitute essential characteristics of either the generic or specific aspects of this invention and, therefore, such adaptations should be, and are intended to be, comprehended within the meaning and range of equivalency of the following claims.

Having thus revealed this invention, I claim as new and desire to secure the following combinations and elements, or equivalents thereof, by Letters Patent of the United States:

1. In a machine tool the combination of a work support a relatively shiftable tool support, means for shifting the tool support relative to the work support selectively in two different directions including a rotatable and normally nonshiftable feed screw and cooperating nut mechanism operatively connected with the shiftable support for shifting said tool support in one of said directions, additional means for shifting said tool support in another of said directions, said additional means being normally inelfective, means comprising a rotatable but nonshiftable drive sleeve for rotating said screw relative to said nut, relatively fixed abutment means interposed in the path of movement of the shiftable support operative to bring said shiftable support to a positive stop when said screw and nut mechanism has traveled said support a preselected distance, means bet-ween said sleeve member and said screw operative normally to restrain said screw against axial movement relative to the sleeve under all power loads required to move the shiftable support and operative when the support engages said abutment and is stopped thereby to permit said screw to move axially relative to the sleeve, and means responsive to said axial yield of the feed screw to suspend the rotation of said sleeve and to render effective said additional means for shifting said tool support so that said tool support is moved first in one direction until brought to a positive stop and thereafter in another and different direction.

2. In a bobbing machine the combination of a rotatable work support a relatively shiftable hob support, means for shifting the hob support relative to the work support selectively radially thereof and in a transverse direction, including a rotatable and axially movable feed screw and cooperating nut mechanism operatively connected with the hob support for shifting the hob support in said radial direction, additional means for shifting said hob support in said transverse direction, means comprising a rotatable but nonshiftable drive sleeve for rotating said screw relative to said nut, relatively fixed abutment means interposed in the path of movement of the hob support operative to bring said hob support to a positive stop when said screw and nut mechanism has traveled said support a preselected distance in a radial direction, means between said sleeve member and said screw operative normally to restrain said screw against axial movement relative to the sleeve under all power loads required to move the hob support in said radial direction and operative when the said support engages said abutment and is stopped thereby to yield axially relative to the sleeve, and means responsive to said axial yield of said feed screw to suspend the rotation of said sleeve and to render said additional means effective to shift said hob support in said transverse direction.

' 3. he combination of claim 2 in which the means for shifting the hob support electively radially of the work support and in a transverse direction are constructed to shift the hob in said directions at two different rates so that the hob is moved radially of the work support at one rate and transversely thereof at another rate.

4. A bobbing machine having in combination a rotatable work spindle and a cooperatively positioned rotatable hob spindle, means to rotate said spindle, means to shift one of said spindles relative to the other electively in one of two different directions comprising a feed screw and nut mechanism operatively associated with the said shiftable spindle for moving the spindle in one direction and a feed screw and nut mechanism operatively connected with the shiftable spindle for moving the spindle in the other of said directions, power means common to both of said screw and nut mechanisms for driving same, clutch means in the drive between said common power means and each of screw and nut mechanisms, adjustable abutment means interposed in the path of movement of the shiftable spindle in response to the operation of one of said screw and nut mechanisms operative normally to stop the movement at a predetermined point, and means responsive to the stopping of spindle movement in one direction and operatively connected with each of said clutch means to disengage the power drive to one of said screw and nut mechanisms and to engage the power drive to the other of said screw and nut mechanisms so that the shiftable spindle is caused to move in one direction until stopped by said abutment means and thereupon caused to move in the other of said directions.

5. The combination of claim 4 in which said power means and said screw and nut mechanisms are constructed and arranged to move the shiftable spindle at a feed rate suitable for the hobbing operation and including additional means operative at the conclusion of the hobbing operation to actuate said screw and nut at a traverse rate in their respective opposite directions to return the shiftable spindle to the starting position.

6. In a hobbing machine having a rotatable work spindle and a rotatable and shiftable hob spindle and power means to shift the hob spindle relative to the work spindle selectively in radial and axial paths at feeding rates and at traverse rates and in opposite directions in each of said paths, the combination of a two-position feed-andtraverse clutch and a two-position direction-control clutch and a two-position feed rate clutch operatively connected with the said power means for shifting the hob spindle for rendering said power means selectively efiective and inellective to shift the hob spindle at a selected rate and in a selected direction, electrically actuated means for actuating each of said clutches, control means for said electrically actuated means including a multicontact stepping switch having successive terminals connected with each of said electrically actuated means and normally operative when said rotary switch is stepped to activate said electrically actuated means sequentially whereby to cause the said clutches to become effective in a prearranged sequence, and means responsive to the linear move ment imparted to the hob spindle by said power means to step the stepping switch.

7. A hobbing machine having a work spindle and a hob spindle adapted to be driven in timed relation the combination of means for moving the hob selectively radially of the work spindle and axially thereof at feed and traverse rates and in opposite directions in each of said radial and axial paths of movement including a feed-traverse selector clutch and a radial-axial direction selector clutch and a feed-rate selector clutch selectively operable to effect movement of the hob spindle in the named directions and at a traverse rate or at a selected feed rate in the selected direction, actuating means for each of said clutches, control means for said clutch actuating means comprising a master selector unit adapted to render each of said clutch-actuating means selectively efiective and inelfective in performing their respective functions, said master selector unit having a multistation movable element adapted upon movement from station-to-station to render the respective actuating means of each of said selector clutches effective in a predetermined sequence, and means responsive to the movement of the hob spindle for actuating the movable element of said master selector unit from station-to-station automatically to control the rate and direction of movement of the hob spindle in said radial and axial paths.

8. The combination of claim 7 including means separate from said master control unit for changing the order of response of said selector clutches to the station-tostation movement of the movable element of the master control unit.

9. In a bobbing machine the combination of a work support a relatively shiftable hob support, means for shifting the support relative to the work support including a rotatable and axially movable feed screw and cooperating nut mechanism operatively connected with the shiftable support, means comprising a rotatable but nonshiftable drive sleeve surrounding a portion of said feed screw for rotating said screw relative to said nut, relatively fixed abutment means interposed in the path of movement of the hob support operative to bring said hob support to a positive stop when said screw has traveled said support a preselected distance, compression spring means between said sleeve member and said screw operative normally to restrain said screw against axial movement relative to the sleeve and operative when the support engages said abutment and is stopped thereby to permit said screw to move axially relative to the sleeve, and means responsive to said axial movement of the feed screw to suspend the rotation of said sleeve.

10. In a machine tool the combination of a stationary support, a relatively shiftable tool support mounted on the said stationary support, means for shifting the tool support along the stationary support comprising cooperating screw and nut elements in which the nut element is mounted in fixed relation to the shiftable support and the said screw element is rotatably journaled to said stationary support, means for rotating said screw element including a drive sleeve rotatably but non-shiftably journaled to said stationary support and telescoping a portion of the screw element, said sleeve element having a splined connection with said screw element so that the screw rotates with the sleeve, means mounting the screw element to the sleeve for limited axial movement relative to the sleeve comprising spring means pre-stressed to restrain the screw against axial movement relative to the drive sleeve under all power loads required to move the shift screw element relative to the drive sleeve to suspend the able support, adjustable abutment means interposed in action of the said means for rotating the screw element. the path of movement of the shiftable support for posi- References Cited in the file of this patent tively stopping the movement thereof at a precise point whereupon said means mounting said screw element for UNITED STATES PATENTS limited axial movement relative to the drive sleeve func- 1,870,793 Collins Aug. 9, 1932 tions to permit the screw to shift axially relative to the 2,368,408 Brooking Jan. 30, 1945 drive sleeve, and means operatively associated with the 2,417,434 Mead et a1 Mar. 18, 1947 stationary support and responsive to the axial shift of the 2,837,010 Davenport June 3, 1958 

